Guilin Sun
Ansys Employee

This indicates that the simulation suffers the so called "late time divergence". For single bus ring resonators, since only one bus for in-out, less light can be coupled out in early simulation, it needs longger simulation time, and thicker PML. Please increase the PML number and make sure the total thickness is roughly half-wavelength.

 

In addition, make the bus waveguide long enough to extend outside of PML.